1. Field of the Invention
The present invention relates a tool assembly, more particularly, to a tool assembly in which a working member is securely coupled with a coupling member and a torque can be transmitted to a working member without a loss.
2. Description of the Related Art
In general, a cutting tool is used in the field of cutting machining such as drilling, milling, and turning. Within the fields of drilling and milling, a tool having a rotary character is useful for machining a fixed and movable workpiece, and a tool for turning machining is fixed and has the purpose of machining work-piece which is rotating.
Conventionally, a drilling tool is divided into a coupling member and a working member the coupling member to be coupled to a driving shaft of a driving mean is compatible with a certain type of machine tool or a tool holder. That is, the coupling member has a shape corresponding to that of the tool holder.
The working member comprises a head oil which chip channels and cooling-medium channels are formed, and cutting inserts are detachably mounted to a front end of the head.
The working member and the coupling member are permanently coupled with each other through an interface between the coupling member and a male spigot that is a rear end portion of the working member. Male-female joints which are fit in a press-fit manner are used as the permanent coupling means between the male spigot and the coupling member.
More precisely, the male spigot that is a rear end portion of the working member is pressed into a seating portion formed at a front end of the coupling member when the seating portion is widened by heating. The coupling member is then cooled and shrunk, and so the coupling member and the male spigot (that is, the working member) are coupled.
In order to transmit the requisite torque between the seating portion of the coupling member and the male spigot of the working member with a sufficient safety margin, a sufficient large contact area should be existed between the male spigot and the seating portion. To secure the above contact area, the male spigot and the seating portion should have a considerable axial extension.
Accordingly, in most cases, an axial length of the mal spigot of the working member is at least 1.5 times greater than a diameter of the head. The fact that the male spigot has the considerable length means that the drilling tool has a great total length.
The tool assembly having the great length has the problems of a great dead weight, a high consumption of material in the manufacturing process and an extra great space in connection with storage and transportation. In addition, the great length of the tool assembly means that the tool assembly is set in a vibration circumstance during the machining process.
In order to solve the above mentioned problems, it is desirable to reduce a total length of the drilling tool as much as possible. Accordingly, the study has been recently made to reduce a length of the male spigot of the working member and a female seating portion of the coupling member while a torque transmission performance between the coupling member and the working member is maintained.